1. Field
The present invention relates to a method of generating a walking pattern for a humanoid robot, and more particularly to a method of generating a walking pattern for a humanoid robot which can walk in an omnidirection and with different strides.
2. Background
A humanoid robot has been developed for human's convenience in the human environment. Researches on the humanoid robot have been done about balancing, walking pattern generation, motion generation, whole body cooperation and so on. In particular, many walking pattern generation methods have been developed to prevent a robot from tipping over. Such methods of generating a walking pattern for a humanoid robot may be generally classified into two groups.
First, there is a method using forward dynamics. This method uses a dynamic equation associated with each link and uses information of each link such that a humanoid robot operates while maintaining its upright posture. However, a humanoid robot requires at least twelve degrees of freedom in its two legs in order to accomplish a behavior similar to that of a human. Therefore, a problem exists in that considerable time is spent obtaining proper actions because it requires so much information on each joint and must solve a complex dynamic equation. Further, to generate stable action of a robot, the robot must perform its walk by changing its walking position.
Second, another method using a linear inverted pendulum model uses limited components such as the total angular momentum and a total Center of Mass (“CoM”) which represent the total mass of a humanoid robot as a point mass. The linear inverted pendulum model simplifies the complex dynamic equation of a humanoid robot into a second-order differential equation to generate a walking pattern. This method uses a Zero Moment Point (“ZMP”) and uses it as an index for evaluating the stability of a robot. It can allow the precise walk of a robot by positioning a ZMP within a supporting area made by a robot according to the walk of the robot and presetting the stability of a robot.
Many methods for generating a walking pattern using a linear inverted pendulum model are introduced in following papers: a paper entitled “An Analytical Method on Real-time Gait Planning for a Humanoid Robot” (K. Harada, S. Kajita, K. Kaneko and H. Hirukawa) published in the IEEE-RAS/RAJ Int. Conf on Humanoid Robot, pp. 640-655, 2004; a paper entitled “Biped Walking Pattern Generation by using Preview Control of Zero-Moment Point” (S. Kajita, F. Kanehiro, K. Kaneko, K. Fujiwara, K. Harada, K. Yokoi and H. Hirukawa) published in the proc. of IEEE Int. conf. on Robotics & Automation, pp. 1620-1626, 2003; and a paper entitled “Biped Walking with Variable ZMP, Frictional Constraint and Inverted Pendulum Model” (C. Zhu, Y. Tomizawa, X. Luo and A. Kawamura) published in the pro. of IEEE Int. Conf of Robotics & Biomimetics, pp. 425-430, 2004, etc. However, these methods must have the ZMP information for some time and generate the pattern by using them. Further, there is a problem in the case that the CoM or the ZMP has the initial value in an initial state and the final value in a stop state of a robot with their methods. It takes place many errors of a walking pattern.